Comment 52 for bug 1747463

Doubt the problem is in the amdgpu driver. What about bug in the amd_iommu?
I think this because I tried to switch off external GPU using acpi_call module.
The following command was successful:

    echo '\_SB_.PCI0.VGA.PX02' > /proc/acpi/call

while running kernel with no KMS (no amdgpu). Fan really went silent
after this, but kernel crashed in several seconds in similar way like
with amdgpu and active iommu.

The filesystem is after every crash corrupted. I'm afraid that storage
controller goes through iommu too and crash causes some random writes to
disk :(. But may be I am wrong and this ACPI call is illegal in reality
and amdgpu does something wrong regarding iommu to. Nevertheless amdgpu works
with iommu=off fine. Maybe the problem is with some buggy BIOS/firmware
from vendor.

I will try a newer kernel.